In a conventional single-sheet printer, media is directed through a print cycle which includes picking up a sheet from an input tray, feeding it through the printer, and then expelling it through the printer's output port. Once expelled, sheets fall to an output tray where consecutive sheets are piled one on top of the other so as to form an output stack. Ideally, the sheets fall directly to the output tray, forming a packet of vertically aligned sheets which is stable and easily manipulable.
Sheets expelled by conventional printers, however, rarely fall into an aligned vertical stack. Instead, sheets fall in a somewhat random fashion due to a variety of aerodynamic forces which produce an effect known generally in the industry as "sail". Such sail is most often characterized by a sheet cutting through the air so as to glide in the direction of sheet expulsion, and potentially pass beyond the confines of the output tray. This effect can result in an increasingly destabilized stack, often culminating in sheets spilling onto the floor and requiring that the sheets be restacked by hand.
In the past, the problem of sheet sail has been addressed using a pair of so-called anti-sail wings which act as intermediate sheet support upon expulsion of a sheet. Once the sheet has been fully expelled, the wings are moved oppositely, releasing the sheet in rear-biased fashion so as to allow the sheet to fall more directly to the output tray without the extent of forward momentum which would otherwise exist. Sheets thus fall to define a generally vertical output stack. An arrangement of the type just described is disclosed in U.S. Pat. No. 5,324,020 which is entitled "Paper Stacking System For Printers" and which is commonly owned herewith. The disclosure of that patent is incorporated herein by this reference.
Although the aforementioned system has proven effective in reducing sheet sail, there remains room for improvement. For example, very little has been done to compensate for variations in sheet media size, or for corresponding variations in sail characteristics due to such differently sized sheets. Conventional printers also have failed to efficiently address the problem of progressive stack destabilization, a phenomenon which is related to the posture of expelled sheets within the printer's output tray. Most printers simply employ an output tray with a floor which is sized to support the largest permissible sheet (generally 81/2.times.14-inch). This has involved the use of a large output tray floor which underlies a substantial portion of output sheets, significantly increasing the cost to manufacture, and obstructing access to the printer's input tray. It thus would be desirable to provide a sheet media handling system which reduces the output tray's size, but improves output media support. More particularly, what is needed is a small size output tray which readily is adapted to address variations in output sail characteristics due to changes in sheet media size.